There are only two ways to reach Machu Picchu: train and the Inca Trail. If hiking isn't your style, you can grab a train from Cusco (four hours), Urubamba (two hours and ten minutes) or Ollantaytambo (one hour and 15 minutes). The train will take you to Machu Picchu Pueblo station (also known as Aguas Calientes), where you can then catch a bus to the ruins.
If you are taking the train directly from Cusco, go to the San Pedro Station at the intersection of Cascapara and Santa Clara. PeruRail has two daily departures, a Vistadome, which leaves at 6:00 a.m. and arrives at Aguas Calientes three-and-a-half hours later, and a Backpacker, which leaves at 6:15 a.m. and arrives in four hours.  The Vistadome at $110 is the luxury trip, and includes snacks, beverages and a sky dome (ergo the name).  The Backpacker, at $75 is the budget trip, but still comfortable withal.  The return trips leave at 3:30 p.m. and 3:55 p.m. respectively. There are also morning departures from Aguas Calientes, beginning at 5:45 a.m. Schedules are subject to change, however, so you are best advised to purchase ahead. And be prepared to bring cash--credits cards of any sort are not accepted.
Those who can afford it and want four-star luxury and convenience can take the new Hiram Bingham Deluxe Train, which departs from the city of Poroy, about 20 minutes north of Cusco. This train leaves at 9:00 a.m. and gets to Aguas Calientes at 12:30 p.m. The train, complete with a bar car, is modeled on the classic Orient Express train of its eponymous owner. The $470 price includes exclusive busses to the ruins of Machu Picchu and guided tours.  The trip back includes cocktails and a four-course supper.
Once you are in Aguas Calientes you must head over to the Tourist Information Office at their Plaza de Armas, and purchase two things: 1) a three-day access pass to the ruins, priced at $43, and 2) a round-trip bus pass for $12. The bus itself leaves from the Plaza. Again, no credit cards are accepted, but there are ATMs in the area.
It is possible to walk to the ruins from the train station, but it takes about one to one and a half hours depending on your fitness level, and whether you choose to take the steeper, more direct path, or the roundabout paved road.

Recently, Cusco regional president Hugo Gonzalez proposed raising the entrance fee to $100 for foreigners, a measure which so has been opposed by Peru's tourism minister, Mercedes Araoz.  Meanwhile, Araoz is investigating the possibility of working with the private sector in constructing cable cars to provide more expedient access to Machu Picchu, while recently the mayor of a neighbor pueblo, Santa Teresa, approved the construction of a small bridge crossing over the  Vilcanota  river,  as a means of  increasing  tourism to  the village by providing  alternative  access to Machu Picchu.  Critics have complained that the  bridge will  make regulation  of access  more difficult,  increasing the possibility of environmental damage, as well as facilitating drug trafficking.